The present invention relates generally to stators for vehicle dynamoelectric machines and, in particular, to a stator assembly for a dynamoelectric machine having small slot openings or mini caps that accepts radial insertion of rectangular wire for the stator winding.
Dynamoelectric machines, such as electric motors, or alternators are well-known. Alternators, generally automotive alternators, typically are composed of a stator assembly fixedly supported by an alternator housing and a rotor assembly supported coaxially within the stator assembly. The stator assembly includes a generally cylindrically-shaped stator core having a plurality of core slots formed along the inner surface thereof and a stator coil disposed in the core slots. The core slots define a plurality of teeth therebetween. The teeth are connected to the core by a yoke portion.
The stator coil is formed by connecting a plurality of wires wound thereon, forming stator windings. The stator windings are accommodated at the plurality of core slots in a plurality of radially extending layers, and are formed of slot wire segments that are located in the core slots and of end loop segments that connect two adjacent slot wire segments of a phase and are formed in a predetermined multi-phase (e.g. three or six) winding pattern in the core slots of the stator core.
It is known in the art that in order to increase the output and efficiency of an alternator it is desirable to have stator winding conductors of rectangular-shaped cross sections that have slot wire segments aligned in a radial row in each core slot and whose widths, including any insulation, closely fit to the width of the main portion of the core slots, including any insulation. A slot wire segment width is defined as being closely fit to the width of the main portion of the core slot, if the ratio of the width of the slot wire segment, including any insulation, to the width of the main portion of the core slot, including any insulation, is greater than 0.6. This is advantageous because the larger conductor width reduces the electrical resistance of the stator winding, and therefore reduces the stator conductor power losses. It is also known in the art to provide a stator core with small slot openings at the inner diameter of the core, which reduces the effective air gap, to increase the alternator output. A smaller slot opening also reduces the fluctuation of magnetic flux on the rotor pole surface, which reduces eddy current losses on the rotor pole and therefore increases alternator efficiencies. It is also desirable to ease manufacturing of the stator assembly by having continuous rectangular shaped conductors to eliminate any weld operation required to connect individual U-shaped conductors axially inserted in the core slots. The term, continuous, utilized herein, refers to a conductor that is continuous for at least the majority of one circumferential pass around the stator core. However, these desirable features lead to a design contradiction in that the conductors must be large to lower the electrical resistance, must also fit closely to the width of the core slots, must be continuous conductors, must be inserted into the core slots from a radially inward position and must have a small core slot opening.
Prior art remedies typically attempted to resolve this design contradiction by utilizing continuous conductors that are small enough to enter the slot openings but do not closely fit the width of the core slots. These prior art remedies result in large voids and low slot fill factors, which leads to an alternator with low output and efficiency. Other prior art remedies utilize U-shaped conductors, which are axially inserted into the core slots and then welded together to form the finished stator windings. These other prior art remedies manage to accomplish a high slot fill factor and consequently low resistance, but encounter difficulties in the assembly of multiple insertions and welds. Other prior art remedies utilize a conductor that is inserted into a flat stator core and than the stator core and conductor assembly are coiled into the desirable annular shape. These other prior art remedies manage to accomplish a high slot fill factor and consequently low resistance, but encounter difficulties in the coiling process of the stator core and conductor assembly.
In view of the above discussed problems, it is advantageous to provide a stator having core slots that allow for conductors to be inserted from a radially inward position while also providing smaller core openings, such that a width of the inserted conductors fits closely to a width created by insulation slot liners lining an inner surface of the core slots. As a result, an alternator having high low-rpm performance and high efficiency while also being easy to assemble and manufacture is realized.